Ok, I now have all the new parts installed on my GSR: DC 4-1 header, AEM cold air intake, Greddy Evo2 cat-back, and Carsound cat. The other night my friend pointed out that it sounds like Vtec is engaging at 4,500rpms. I don't have a VAFC so theres no way I could have changed it. I mean @ 4500rpms my engine really opens up. Anyone have an answer for me on whats going on with my car?